1. Field Of The Invention
The present invention relates to rigid foams characterized by carbodiimide, isocyanurate and urethane linkages and improved flame retardancy. More particularly, the invention relates to rigid foams prepared by catalytically condensing (a) an organic polyisocyanate with a polyol or (b) a quasi-prepolymer in the presence of a blowing agent and alumina trihydrate.
2. Prior Art
The preparation of urethane-modified carbodiimideisocyanurate foams is well known in the art. Generally these foams are prepared by the condensation of an organic polyisocyanate in the presence of a polyol, a blowing agent and a catalyst system which promotes the carbodiimide, isocyanurate and urethane reactions. The foams may also be prepared by condensing, in the presence of a blowing agent, a quasi-prepolymer prepared by the reaction of a stoichiometric excess of an organic polyisocyanate with a polyol. Various catalyst systems have been described in the art as useful for the preparation of these foams. Illustrative of the prior art in this area include U.S. Pat. Nos. 3,887,510; 3,891,578; 3,891,579; 3,894,972; 3,922,238; 3,928,256; and 3,981,829. The present invention is directed to an improvement in the process and compositions described in the aforementioned patents.